The world market offers a great variety of coating options to protect the inner surface of pipes used for the transport of fluids from the effects of corrosion and erosion. Some, additionally, exhibit features that allow the reduction of friction and turbulence, thus, increasing the efficiency of flow. Among the alternatives to anticorrosive coatings, one can find those based on liquid epoxy; the epoxy coating is adhered by fusion and the special anticorrosive paints.
Among the main features of these coatings, they exhibit adaptation to corrosive environments, resistance to various solvents and chemical products, as well as to cathodic detachment.
The research on inner coatings along with the technical and metallurgic evolution required by pipes and accessories, has resulted in the development of coating that satisfies all kinds of needs.
A very common kind of coating is cement mortar lining, which fulfills the standards set forth in ISO 4179 and AWWA C104 for use in water distribution systems and sewerage systems. The ceramic epoxy coating for gravity-operated septic tanks and sewerage systems and the special inner coating for specific service conditions.
Inner cement lining is done by making the pipe rotate at high angular velocity coupled with vibration that produces a dense coating.
The high centrifugal speed allows the coating to become smooth, dense and perfectly compact.
The Hazen-Williams formula has determined that the coefficient of friction is 140 for cement linings and 150 for polyethylene and epoxy coatings.
Other anticorrosive and abrasive resistant protections consist in placing plastic liners inside the pipes. However, said liners are not adhered to the metal. They are simply attached at the ends of the pipe to avoid displacement.
Prior art shows a steel pipe inner coating made of high-density consolidated polyethylene. Also, prior art shows a steel pipe with an insulating inner coating and a fiber-filled thermoplastic liner placed inside a steel pipe.
Besides, prior art shows an inner coating for pipes made up of a highly heat-resistant TPU-Polyester lining which allows a nonwoven fabric to be saturated with an epoxy-amine resin and to be cured with steam or hot water.
There is a coating made up of a solixane-based elastomer processable by heat fusion, a coating made of a thermoplastic material, and a thermoplastic coating applied to the inside of the pipe by injecting gas that pushes the material against the inner surface of the pipe.
Even though all the known coatings in the field of technique yield the desired results for their specific purpose, the known coatings do not unfortunately include a plastic coating that can strongly adhere to pipes so that it can withstand pressure drops of the magnitudes present in oil and gas production pipelines.
In addition, the proposed solution in the preceding documents covers coatings with one or at most two external layers so as to obtain the mentioned protection. However, in the case of the present protection, it is made up a three-layer coating wherein each of the layers exhibits features that taken together afford a much superior protection compared to that of solutions in the prior art.
Nor does prior art show a coating that can make pipes impermeable to liquids and gases simultaneously.
In addition to solving the previous points, the proposed invention also shows a yet-inexistent procedure in the prior art, whereby a layer of adhesive thermoplastic is applied between an epoxy adhesive and material of the plastic pipe so as to achieve a full adherence of the various components and steel of the metal pipe.
Finally, neither is there in the state of the art, and the invention does describe this, a procedure that includes a step whereby a plastic pipe is pressed against the surface of the steel pipe, while simultaneously applying heat at a temperature higher than the point of softening of the thermoplastic material, but without damaging the material.